1. Field of the Invention
The present invention relates to a method of manufacturing lens-fitted photo film units and an apparatus therefor. In particular, the present invention relates to a method of making a film roll from a filmstrip that is withdrawn from a cartridge shell, and loading the film roll and the cartridge shell in a film roll chamber and a cartridge chamber of the lens-fitted photo film unit, and an apparatus therefor.
2. Background Arts
Lens-fitted photo film units, hereinafter referred to as film units, contain a film cartridge and have a simple exposure mechanism for taking photographs on a filmstrip of the film cartridge. The filmstrip is previously withdrawn from a cartridge shell and wound into a roll. The film roll and the cartridge shell are loaded in a film roll chamber and a cartridge chamber of the film unit respectively.
Japanese Laid-open Patent Application No. 7-219156 discloses a method of loading a film unit with a new type of film cartridge that contains a filmstrip fully inside a cartridge shell, and can advance the filmstrip to the outside of the cartridge shell in response to a spool being rotated in an unwinding direction. Hereinafter, this new type of film cartridge will be called a leader-advancing type film cartridge. The film loading method according to this prior art is comprised of a first process of advancing the filmstrip a predetermined length out of the cartridge shell by rotating the spool, a second process of winding the filmstrip into a roll by engaging a leading end of the filmstrip with a winding shaft and rotating the winding shaft, a third process of putting the film roll and the cartridge shell in the film roll chamber and the cartridge chamber respectively, and a fourth process of pulling the winding shaft out of the film roll after the rear cover is attached.
The first to fourth processes are carried out in the same place while holding the cartridge shell by the same device. Concretely, a film supply shaft and a winding shaft are placed at a distance that is adjusted to the spacing between the film roll chamber and the cartridge chamber, and the spool of the cartridge shell is engaged with the film supply shaft. By rotating the film supply shaft and hence the spool in the unwinding direction, the filmstrip is advanced out of the cartridge shell. After the leading end of the filmstrip is secured to the winding shaft, the winding shaft starts rotating to wind the filmstrip into a roll, whereas the film supply shaft gets idle. The film roll and the cartridge shell are put in the film roll chamber and the cartridge chamber of the film unit by moving the winding shaft and the film supply shaft while maintaining the spacing between the winding shaft and the film supply shaft.
To secure the leading end to the winding shaft, the leading end of the filmstrip is inserted in a slit of the winding shaft and, thereafter, wound around the winding shaft by rotating the winding shaft. If the leading end of the filmstrip protrudes from the slit, the leading end is bent as the filmstrip is wound tightly around the winding shaft. Since the filmstrip is designed to be fully rewound back into the cartridge shell in the film unit after the completion of exposure of all available frames, it is necessary to advance the exposed filmstrip out of the cartridge shell for development and printing. However, if the leading end of the filmstrip is bent, it is difficult to advance the filmstrip out of the cartridge shell. Therefore, it is important to position the leading end of the filmstrip within the slit of the winding shaft.
To advance the filmstrip by a predetermined length out of the cartridge shell, it is possible to detect the leading end of the filmstrip by a photo sensor. However, since the film leader advancing process and the film winding process are carried out in the same place, the photo sensor must be placed before or behind the winding shaft in the film advancing direction. It is possible to provide a pair of sensors before and behind the winding shaft in the film advancing direction in order to confirm that the leading end of the filmstrip is positioned inside the slit of the winding shaft. In any case, however, the spool of the film cartridge should be rotated with accuracy after the detection of the leading end of the filmstrip by any of the photo sensors in order to stop the leading end inside the slit of the winding shaft. It is also time consuming. Besides, the length of the filmstrip out of the cartridge shell can change after the fine adjustment to the slit, as the filmstrip can uncoil inside the cartridge shell due to its own resiliency.